The field of interest is optical networks, and more specifically, optical switching fabrics.
An optical switching cross-connect comprises equipment that switches or routes information received from one or more fiber optic media input lines, and transmits the information out through one or more fiber optic media output lines. The connecting of input lines to output lines through the optical cross-connect can occur in any combination or permutation.
FIG. 1 shows a general optical cross-connect 100 with an electrical switching fabric. In this prior art embodiment, each incoming line 102 is fed into the demultiplexer section 104 wherein a demultiplexer 106 separates the multiple wavelengths on each incoming line. In a central portion 108 optical-to-electrical translation of incoming optical signals is accomplished, followed by the switching, which is accomplished electrically. The electrical switching fabric output is then converted via electrical-to-optical translation to optical signals. Finally, each multiplexer 112 in the multiplexer section 110 places several wavelengths onto an output optical transmission line 114.
FIG. 2 (prior art) shows a conventional electrical-to-optical (EO) conversion 200. Each input line 202, typically carrying an optical signal comprising information on a single wavelength carrier, is connected to an optical receiver 204, which translates the optical signals received on the input line into electrical signals. An electrical switching fabric 206 routes each electrical signal to its intended output line 208. The electrical signal output from the electrical switching fabric 206 is then fed to an optical transmitter 210, where the electrical signal modulates an optical laser carrier beam generated by a laser within the optical transmitter. The output of the optical transmitter 210 is fed into an optical transmission line 212, which is typically a fiber optic cable.
FIG. 3 (prior art) shows a typical optical laser transmitter module 300, the module comprising a Continuous Wave (CW) fixed International Telecommunications Union (ITU) grid wavelength laser 302, and an external modulator 304 that modulates the laser carrier beam with information from an Electrical Data Input 306, which data has come from the electrical switching fabric 206 (see FIG. 2). A tap 312 diverts some of the light energy emitted from the laser to a wavelength locker 314, which provides feedback to control circuitry 316 that serves to maintain a specific wavelength of the ITU grid wavelength laser 302. Monitoring circuitry 318 monitors the wavelength and power of the ITU grid wavelength laser 302.
As seen in FIG. 2, prior art EO conversion employs one optical transmitter 210 for each output line coming from the electrical switching fabric 206. Prior art further depicted in FIG. 3 shows that each optical transmitter contains at least one laser that supplies the optical carrier to be modulated by the external modulator 304, which is then output to an Optical Data Output 310.
Optical cross-connect architecture comprises both optical and electrical switching fabrics. Electrical switching fabrics require optical-to-electrical (OE) conversion circuitry and electrical-to-optical (EO) conversion circuitry. In designing electrical switching fabrics, EO conversion circuitry is the predominant cost factor. Reducing costs of EO conversion circuitry would have a major impact on overall cost of an electrical switching fabric-based optical cross-connect installation. The set of lasers providing output carrier beams to the output modulators is a major expenditure in EO conversion. A reduction in the total number of lasers needed to produce all output channels would result in a significant cost saving.
Method and apparatus is provided for supplying output carrier optical signals to output modulators through the use of a reduced number of lasers that comprise a shared laser bank. The total number of lasers employed is less than the total number of optical modulators being supplied with optical carriers.